1. Field of the Invention
The present invention relates to a paper-feeding apparatus and a method of feeding paper.
2. Description of the Related Art
Conventional paper-feeding apparatuses are of a construction where a platform or sheet guide frame is pushed upward by the urging force of a pressure spring so that the print medium placed on the platform is pressed against a feeding roller. A controller provides an instruction to a paper-feeding motor and the paper-feeding motor drives the feeding roller into rotation to advance the print medium from the platform.
When feeding the print medium from the platform, a plurality of pages of print medium may be advanced simultaneously by chance from the platform. In order to prevent such a simultaneous advancement of pages, a separator wall is provided which is formed of a film and located at the forward end of the platform. The separator wall obstructs the plurality of pages and allows only the top page to be fed. There is also provided a brake shoe formed of a foamed material that opposes the feeding roller, and the forward end of the print medium is allowed to abut the brake shoe. The top page of the print medium is advanced by a frictional force between the feeding roller and the print medium and the following pages are trapped by the rough surface of the brake shoe.
One conventional paper-feeding apparatus is provided with a cam mechanism provided at each longitudinal end of a shaft of the feeding roller. The platform is moved upward and downward as the feeding roller rotates. When not feeding the print medium, the platform is moved away from the feeding roller so that a user can easily place a stack of print medium into the platform. The platform does not exert any load on the print medium when the print medium is being advanced by a main feeding roller once the print medium has been fed by the feeding roller.
Another conventional paper feeding apparatus is provided with a feeding roller having a D-shaped cross-section. In other words, the feeding roller is generally a deformed cylinder that has been partially cut away in a plane parallel to a longitudinal axis of the cylinder. When not feeding the print medium, the flat surface of the feeding roller opposes the brake shoe, creating a gap between the flat surface and the brake shoe. Thus, the feeding roller is not in contact with the print medium and does not interfere with the print medium being advanced from the platform.
The feeding roller has idle rollers that have a smaller diameter smaller than the feeding roller and freely rotate on the shaft of the feeding roller. When the flat surface of the feeding roller opposes the brake shoe, the idle rollers are brought into contact with the brake shoe, thereby preventing the print medium placed on the platform from being advanced inadvertently.
However, the aforementioned conventional paper-feeding apparatuses cannot ensure that print medium of various kinds such as thin paper, thick paper, envelopes and so on is advanced one page at a time. In general, a plurality of pages tend to be advanced simultaneously when thin print medium is fed while paper feeding often fails when thick print medium is fed.
Pressing the brake shoe against the feeding roller with a larger force in an attempt to prevent multi-page feeding will cause failure of a paper feeding operation if the print medium is thick. Pressing the brake shoe against the feeding roller with a smaller force in an attempt to prevent failure of a paper feeding operation will cause multi-page feeding.